Patch antenna with switchable reactive components for multiple frequency use in mobile communications

ABSTRACT

The apparatus ( 100 ) comprises a printed circuit board ( 20 ) on which an antenna device ( 10 ) is present. The antenna ( 2 ) of the antenna device ( 10 ) can be tuned by means of matching bridges ( 34, 37 ), each of which comprise a reactive component ( 3,4 ) and a switch ( 25, 26 ). Preferably, the switches ( 25,26 ) are located outside the antenna device ( 10 ) such that a standardized antenna device ( 10 ) can be used.

[0001] The invention relates to an apparatus with a radio communicationfunction, comprising a carrier having a first and an opposite, secondside and provided with a ground conductor, at which first side anantenna device is present, which antenna device comprises a substratehaving a first and an opposite, second side and an antenna present atthe first side of the substrate and having an input impedance, theapparatus further comprising means for tuning said input impedance.

[0002] The invention also relates to an antenna device.

[0003] The invention further relates to a carrier having a first and anopposite, second side and provided with a ground conductor.

[0004] The invention also to a method of tuning an antenna of anapparatus with a radio communication function, which apparatus comprisesa carrier with a ground conductor and an antenna device comprising asubstrate and the antenna, which method comprises the steps of measuringan input impedance and adapting the input impedance.

[0005] Such an apparatus, such an antenna device and such a method areknown from WO-A 00/03453. The known antenna is of the PIFA type andsubstantially consists of a metal strip. The metal strip of the knownantenna device is provided with ground terminal and an input terminal.Between said terminal a matching bridge is present. Tuning of theantenna is performed by measuring or estimating the input impedanceassociated with the antenna and subsequently matching the inputimpedance through adjustment of the length of the matching bridge.Tuning of the antenna is necessary for each specific application, i.e.each apparatus with its own design.

[0006] It is a disadvantage of the known antenna device that it must bemodified for each application. This precludes the use of standardizedantenna devices.

[0007] It is therefore a first object of the invention to provide anapparatus of the kind mentioned in the opening paragraph of which theantenna can be tuned without significant modification of the antennadevice.

[0008] It is a second object of the invention to provide an antennadevice of the kind mentioned in the opening paragraph which can be usedin various applications without any further substantial modifications.

[0009] It is a third object of the invention to provide a carrier thatcan be used in the apparatus of the invention.

[0010] It is a fourth object of the invention to provide a method of thekind mentioned in the opening paragraph, by which the antenna can betuned without significant modification of the antenna device.

[0011] The first object is achieved in that said means comprise a firstand a second matching bridge that comprise a reactive component and aswitch, and that are connected between the antenna and the groundconductor. In the present invention, the input impedance is adjusted byswitching at least one of the switches on or off. Due to the inclusionof the switch in each of the matching bridges, the matching of the inputimpedance is converted from an analogue into a digital operation.Although the number of matching bridges can be relatively small, theresulting tuning is sufficiently good. Furthermore, the inclusion of theswitch in each of the matching bridges allows the provision of theswitch in a different location than the reactive component. Inparticular the switch is provided in a location, where it is wellaccessible after the antenna device has been placed on the carrier, forinstance a printed circuit board. Such location are, for example, anouter surface of the printed circuit board and an outer surface of theantenna device.

[0012] If the reactive components are capacitors, the matching bridgesare connected in parallel. The matching bridges with capacitors can beattached to the antenna in any location, but preferably are attached toone end of the antenna, whereas a ground terminal connecting the antennato ground is present at another end of the antenna. If the antenna is ofthe patch or PIFA type, the capacitors preferably comprise a dielectricmaterial with a relatively high dielectric constant. Capacitors with adielectric constant of about 80 relative to vacuum and with a goodtemperature stability of the capacitance are commercially available. Ifthe reactive components are inductors, they are preferably connected inseries, whereas the switches of the matching bridges are connected inparallel.

[0013] In a preferred embodiment, the reactive components of the firstand second matching bridges are capacitors, and the matching bridges areconnected in parallel. This has the advantage that the input impedancecan be tuned over a relatively broad range. If, for example, a first, asecond and a third matching bridge are present and—as is preferable—thereactive components each have a different value, the input impedance canbe adjusted to eight different values.

[0014] In a further preferred embodiment, a resonant circuit isconnected between the antenna and the ground conductor. It has beenobserved that the presence of a resonant circuit provides a greaterbandwidth. An advantage of this is that less tuning is necessary.Another advantage is that the combined presence of a greater bandwidthand the matching bridges allows the matching bridges to be used forfine-tuning. The reactive components may be chosen accordingly. Afurther advantage is that due to the connection of the resonant circuitthe behavior of the antenna is modified so as to provide a dual bandoperation without the need for switching. Such is known from thenon-prepublished application with number GB0013156.5 (PHGB000065).

[0015] The matching bridges may be present at the carrier, from wherethey are connected to one point on the antenna. Alternatively, thematching bridges may be present at the antenna device and are connectedto the ground conductor through a single connection to the printedcircuit board. Furthermore, an extension of the ground conductor may bepresent in the antenna device, for example in the substrate. It ispreferable however that a first module contact pad forming part of thefirst matching bridge and a second module contact pad forming part ofthe second matching bridge are present at the second side of thesubstrate; and that a first board contact pad forming part of the firstmatching bridge and a second board contact pad forming part of thesecond matching bridge are present at the first side of the carrier. Inthis embodiment, connections to the ground conductor at the carrier areindividualized. An advantage of this embodiment is that a standardizedantenna device can be used for many applications. Said contact pads arepreferably part of Ball Grid Arrays or Land Grid Arrays, so that a boardcontact pad and a complementary module contact pad are connected withoutan additional manufacturing step.

[0016] Any component with which the matching bridge can be disconnectedor connected at least once may be used a switch. Electrically drivenswitches such as micro-electromechanical switches, actuators andtransistors may be used. The switches may also be embodied so as to beremotely controlled, for example in response to a radio wave receivingstate. In this embodiment, the remote, controlling part of the switch iseasily accessible, whereas the actual switching part is providedanywhere in- or outside the antenna device.

[0017] Furthermore, the switch may be embodied as a track, for example atrack of which the conductivity can be changed with laser radiation.This track may contain a material having an amorphous and a crystallinestate, such as the material aluminum-germanium.

[0018] In an advantageous embodiment, the switch substantially consistsof a conductive track that can be cut through mechanically, opticallyor—as a fuse—electrically. Such a switch may be integrated in thepattern of conductive tracks at an outer surface of the carrier.Dimensions of the conductive track acting as a switch will depend on theapplication and the way of disconnecting. In an alternative embodiment,the switch consists of a pair of component pads at the carrier. Byplacing an SMD-component with a minimal resistance onto said componentpads, a matching bridge is electrically connected to the printed circuitboard. The apparatus according to claim 9 is provided as a result ofsuch a once-only switchable switch.

[0019] In a preferred embodiment, the switches of the matching bridgesare present on the first side of the carrier and located such that thereis a zero overlap between a perpendicular projection of the antennadevice onto the printed circuit board and the switches. The carrier isfor instance a printed circuit board, but can be any other type ofsubstrate, such as a multilayer ceramic substrate. A first advantage ofthe embodiment is that the carrier has a surface that is well accessiblefor the major part. A manufacturer of the apparatus of the invention canadjust the input impedance of the antenna by modifying the printedcircuit board. A second advantage is that the matching bridges can beused by an antenna designer as additional means for providing anexcellent antenna, next to the modification of the metal strip of theantenna and the location of terminals at the antenna.

[0020] In another embodiment, the switches of the matching bridges arepresent at the second side of the carrier, and a via is present betweenthe switch and the board contact pad within each of the matchingbridges. As the switches are present at the second side of the carrier,the surface of the carrier can be used in a very efficient manner, or itcan be miniaturized. In this embodiment, the switches may also be usedas the only means, or alternatively as additional means for tuning ofthe antenna. In this embodiment it is preferable that the groundconductor is also present at the second side of the carrier.

[0021] In a further embodiment, the reactive components are present inthe antenna device. An advantage of this embodiment is that themanufacturer of the carrier, esp. the printed circuit board, does notneed to understand the matching of the impedance; device the reactivecomponents and their impedances are chosen in the design of the antenna.The reactive components may be implemented as discrete components, ormay alternatively be integrated into an array of passive components orinto the substrate—for example in a Low Temperature Co-fired Ceramic orLTCC substrate.

[0022] In a still further embodiment, the reactive components areintegrated into an array of passive components. The integration of thereactive components leads to miniaturisation and to a reduction inassembly cost. Alternatively, the replacement of discrete componentswith an array offers the possibility to increase the number of reactivecomponents, and hence to improve the tuning of the antenna. Furthermore,the reactive components in an array can be easily interconnected, thusproviding the option of matching bridges with more than one reactivecomponent. In comparison with the integration of reactive components inthe substrate, it is the advantage of an array that a dielectricmaterial with a high dielectric constant can be used for the capacitorsand that the components have a very high precision.

[0023] In an advantageous embodiment, the antenna device comprises anintegrated circuit and a number of passive components. An example ofsuch an antenna device is a radio module suitable for communicationaccording to the Bluetooth™ standard. The passive components presentare, for example, a balun, a bandpass filter, a VCO resonator. Theintegrated circuit, for example, implemented as a transceiver. As theantenna device of this embodiment already comprises passive components,the introduction of the reactive components of the matching bridges doesnot give rise to additional process steps in the manufacture of thedevice. It further offers ample possibilities to integrate severalindividual reactive components into passive networks. Furthermore, saidantenna device can be considered to be a true plug-and-play device andis suitable for various apparatuses such as telecellular phones, laptopcomputers, personal digital assistants, and other electronic consumerdevices.

[0024] The second object is realized in an antenna device suitable foruse in the apparatus as claimed in to any of the claims 1 to 8.

[0025] It is advantageous especially for a complex antenna devicecomprising an integrated circuit and a number of passive components thatit can be manufactured in a standardized manner, and that anymodification necessary for tuning the antenna is embodied outside theantenna device.

[0026] The third object is realized in a carrier suitable for use in theapparatus as claimed in to any of the claims 2 to 8, having a first andan opposite, second side and provided with a ground conductor, at whichfirst side a first and a second board contact pad are present, whichfirst and second contact pads are connected to the ground conductor viaa first and a second switch, respectively.

[0027] The fourth object of the invention to provide a method of thekind mentioned in the opening paragraph, by which the antenna can betuned without significant modification of the antenna device, isrealized in that a first and a second matching bridge are presentbetween at least one point on the antenna and at least one point on theground conductor, each of said matching bridges comprising a reactivecomponent and a switch, and in that the input impedance of the antennais adapted through switching on or off at least one of said switches.

[0028] These and other aspects of the apparatus, the antenna device andthe method according to the invention will be further elucidated withreference to the figures, in which:

[0029]FIG. 1 is a cross-section al view of a first embodiment of theapparatus;

[0030]FIG. 2 is a block diagram of the first embodiment of theapparatus;

[0031]FIG. 3 is a diagrammatic bottom view of the first embodiment ofthe apparatus;

[0032]FIG. 4 is a cross-section al view of a second embodiment of theapparatus;

[0033]FIG. 5 is a diagrammatic plan view of the second embodiment of theapparatus; and

[0034]FIG. 6 is a diagrammatic plan view of the apparatus after tuningand redesign.

[0035]FIG. 1 shows a first embodiment of the apparatus 100 of theinvention. The apparatus 10 comprises a printed circuit board 20 with afirst side 28 and a second side 29. The printed circuit board 20comprises a ground conductor 21 at its second side 29. An antenna device10 is provided on the first side 28 of the printed circuit board 20. Theantenna device 10 comprises a substrate 1 with a first side 8 and withan opposite, second side 9. On the first side 8 of the substrate 1 areprovided an patch antenna 2, an integrated circuit 11, and reactivecomponents 3,4. In this embodiment, the patch antenna 2 is U-shaped andis connected to the substrate 1 by two opposite side faces 91, 92.Alternatively, a construction may be used wherein the patch antenna 2 isconnected to the substrate 1 at one side face only. Preferably, theantenna device 10 comprises further components as indicated in FIG. 2.The antenna 2 can be connected to the ground conductor 21 via thereactive components 3,4. For this purpose there are electricallyconducting connections from each of the reactive components 3,4 to anumber of switches 25, 26 which are present at the second side 29 of theprinted circuit board 20. Each of the connections comprises a via 5through the substrate 1 of the antenna device 10, a module contact pad7, 47, a board contact pad 22, 46, and a via 23 through the printedcircuit board 20.

[0036]FIG. 2 is a block diagram of the antenna device 10 according tothe first embodiment of the apparatus 100 of the invention. The antennadevice comprises an integrated circuit 11 provided with six inputterminals 19. The integrated circuit functions as a transceiver. Coupledto the integrated circuit 11 are a VCO tank 16, a PLL loop filter 17,and a supply decoupling unit 18. The transceiver can transmit signals tothe antenna 2 and receive signals from the antenna 2. A TX/RX switch 14is provided or changing from the receiving to the transmitting functionand vice versa. The TX/RX switch 14 directs signals via the RX balunfilter 12 to the integrated circuit 11. The signals transmitted from theintegrated circuit 11 go via the TX balun filter 13, the TX/RX switch14, and a bandpass filter 15 to the antenna 2. The antenna 2 is for thispurpose provided with an input terminal 31. The antenna is furtherprovided with a ground terminal 32 and with matching bridge terminals33. In this example, four matching bridges 34, 35, 36, 37 are provided,each of which contains a capacitor 3 i.e. 3 a, 3 b, 3 c, and 3 d,respectively and a switch 25, i.e. 25 a, 25 b, 25 c, and 25 d,respectively, which switch 25 is located outside the antenna device 10.These matching bridges 34, 35, 36, 37 are connected to matching bridgeterminals 33. The ground terminal 32 is further connected to the groundconductor. Parallel to said connection between the ground terminal 32and ground conductor 21, there is a resonant circuit 51 containing acapacitor 52 and an inductor 53.

[0037] The antenna device is adapted for Bluetooth applications having astandard frequency of 2.5 GHz and functions as follows. The patchantenna 2 has a length of 10 mm with an inductance of 1 nH/mm. The patchantenna 2 further has a capacitance value of 0.1 pF. If none of theswitches 25 in the matching bridges 34-37 are closed, the resultingfrequency is 5.0 GHz. The capacitors 3 a, 3 b, 3 c, and 3 d have causescapacitance values of 0.1, 0.3, 1.0 and 2.5 pF. Switching-on of anadditional capacitance of 0.1 pF causes the frequency to be 3.5 GHz,with an additional capacitance of 0.3 pF the frequency is 2.5 GHz, with1.3 pF the frequency is 1.3 GHz, and with 3.8 pF the frequency is 0.8GHz. In this manner the frequency can be adjusted between 0.8 GHz and 5GHz. Alternatively, the frequency can be tuned to 2.5 GHz if it is foundbefore tuning that the actual frequency deviates from 2.5 GHz. Fortuning the frequency downwards, switches have to be turned on; fortuning the frequency upwards, switches have to be turned off. It istherefore preferred to start with one switch on, such that one matchingbridge with a capacitor having an intermediate capacitance of 0.3 pF isconnected to the ground conductor 21. For example, the switch 25 b ofmatching bridge 35 with a capacitor of 0.3 pF could be turned on. Bychoosing a suitable combination of switched—on capacitors, otherfrequencies in between of those mentioned can be realized. The frequencyspectrum can be broadened due to the resonant circuit 51. Preferably,the capacitors 3 comply with the NPO-standard, which standard statesthat the temperature dependence of the capacitance is in the range of−30 to +30 ppm/° C.

[0038]FIG. 3 is a bottom view of the printed circuit board 20. In thisbottom view, the second side 29 of the printed circuit board is shown,provided with the ground conductor 21 and the switches 25 a, 25 b, 25 c,and 25 d. In order to disconnect any of the corresponding matchingbridges 34, 35, 36, and 37, a switch must be cut through or be destroyedwith a laser.

[0039]FIG. 4 is a cross-section al view of a second embodiment of theapparatus 100 of the invention. The apparatus 100 comprises a printedcircuit board 20 with a first side 28 and a second side 29. The printedcircuit board 20 comprises two insulating layers 41,42 between which aground conductor 21 is provided. At the first side of the printedcircuit board, a pattern of conductive tracks is provided, comprisingboard contact pads 22, 46, interconnects 43, via pads 44, and switches25, 26, 27, of which in FIG. 4 only switches 25 and 27 are shown. Theswitches 25,26,27 are embodied as a pair of pads on which an SMDcomponent with a zero or low resistance can be placed to provide aconnection. An antenna device 50 is provided on the first side 28 of theprinted circuit board 20. The antenna device 50 comprises a substrate 1with a first side 8 and a second side 9. A patch antenna 2 having anearth terminal 32, a matching bridge terminal 33, and an input terminal31 (not shown) is provided at the second side. The substrate furthercontains reactive components 3 and 4 (not shown) and interconnects 6from the matching bridge terminal 33 to the reactive components 3. Vias5 are present in the substrate 1.

[0040]FIG. 5 is a plan view of the second embodiment of the apparatus100 of the invention. The patch antenna 2 has a spiral shape with theground terminal 32 at one end and connected thereto the matching bridges37, 38, and matching bridge terminals 33 at the other end, with matchingbridges 34, 35, 36, 39. Also provided is an input terminal 3, throughwhich the antenna 2 communicates with a receiving and transmittingcircuit. The reactive components 3, 4 are present on the substrate 1 ofthe antenna device 50. The switches 25, 26, 27 are present on the firstside 28 of the printed circuit board 20. The switches 25,26,27 areembodied as a pair of pads on which an SMD component with a zero or lowresistance can be placed to provide a connection.

[0041]FIG. 6 is a plan view of the apparatus 110 of the invention. Thisapparatus 110 results from a redesign of the printed circuit board 20after tuning of the antenna 2 by means of the matching bridges 34-39.The antenna device 50 has not been changed in this redesign. This hasthe advantage that the antenna device 50 can be manufactured accordingto a standardized design. In the apparatus of the invention, thematching bridges 34-39 do not contain switches any more. Instead, someof them, such as the matching bridges 34, 36 and 38, are connected tothe ground conductor 21, whereas others are not.

1. An apparatus (100) with a radio communication function, comprising acarrier (20) having a first (28) and an opposite, second side (29) andprovided with a ground conductor (21), at which first side (28) anantenna device (10,50) is present, which antenna device (10,50)comprises a substrate (1) having a first (8) and an opposite, secondside (9) and an antenna (2), present at the first side (8) of thesubstrate (1) and having an input impedance, the apparatus (100) furthercomprising means for tuning said input impedance, characterized in thatsaid means comprise a first and a second matching bridge (34, 37) thatcomprise a reactive component (3,4) and a switch (25, 26), and that areconnected between the antenna (2) and the ground conductor (21).
 2. Anapparatus (100) as claimed in claim 1, characterized in that a firstmodule contact pad (7) forming part of the first matching bridge (34)and a second module contact pad (47) forming part of the second matchingbridge (37) are present at the second side (9) of the substrate (1); anda first board contact pad (22) forming part of the first matching bridge(34) and a second board contact pad (46) forming part of the secondmatching bridge (37) are present at the first side of the carrier.
 3. Anapparatus (100) as claimed in claim 2, characterized in that theswitches (25, 26) of the matching bridges (34, 37) are present on thefirst side (28) of the carrier (20), and the switches (25, 26) arelocated such that there is no overlap between a perpendicular projectionof the antenna device (10,50) onto the carrier (20) and the switches(25, 26).
 4. An apparatus (100) as claimed in claim 1, characterized inthat the reactive components (3) of the first and the second matchingbridges (34, 35) are capacitors.
 5. An apparatus (100) as claimed inclaim 1, characterized that a resonant circuit (51) is present betweenthe antenna (2) and the ground conductor (21).
 6. An apparatus (100) asclaimed in claim 2, 3 or 4, characterized in that the reactivecomponents (3,4) are present in the antenna device.
 7. An apparatus(100) as claimed in claim 6, characterized in that the reactivecomponents (3,4) are present on the substrate (1) and are integratedinto an array of passive components.
 8. An apparatus (100) as claimed inclaim 1, 2 or 5, characterized in that the antenna device (10) comprisesan integrated circuit (11) and a filter (12,13,15,17).
 9. An apparatus(110) with a radio communication function, comprising a carrier (20)with a first (28) and an opposite, second side (29) and provided with aground conductor (21), at which first side (28) an antenna device(10,50) is present, which antenna device (10,50) comprises a substrate(1) having a first (8) and an opposite, second side (9) and an antenna(2) present at the first side (8) of the substrate (1) and having aninput impedance, the apparatus (110) further including means for tuningsaid input impedance, wherein said means comprise a first and a secondmatching bridge (34,37) that are electrically connected to the antenna(2) and are provided with a reactive component (3,4), and at least oneof said bridges (34,37) is electrically connected to the groundconductor (21).
 10. An antenna device (10,50) suitable for use in theapparatus (100, 110) as claimed in any of the claims 1 to 9, comprisinga substrate (1) having a first (8) and an opposite, second side (9), anantenna (2) present at the first side (8) of the substrate (1), andantenna device parts belonging to a first and a second matching bridge(34,37), that are connected to the antenna (2) and is provided with areactive component (3,4).
 11. A carrier (20) suitable for use in theapparatus (100) as claimed in any of the claims 2 to 8, having a first(28) and an opposite, second side (29) and provided with a groundconductor (21), at which first side (28) a first (22) and a second boardcontact pad (46) are present, which first (22) and second contact pads(46) are connected to the ground conductor (21) via a first and a secondswitch (25,26), respectively.
 12. A method of tuning an antenna (2) ofan apparatus (100) with a radio communication function, which apparatus(100) comprises: a carrier (20) with a ground conductor (21), an antennadevice (10,50) comprising a substrate (1) and the antenna (2), and afirst and a second matching bridge (34,37) between at least one point(32,33) on the antenna (2) and at least one point on the groundconductor (21), each of said matching bridges (34,37) comprising areactive component (3,4) and a switch (25,26), which method comprisesthe steps of: measuring an input impedance of the antenna (2); andadapting the input impedance of the antenna (2) by switching at leastone of said switches (25,26) on or off.